Vascular catheters measured blood pressure, for instance, while electrodes secured within the rats' chest cavities provided information about the heart's electrical activity. (Also see "Pictures: How a Python Can Swallow a Crocodile.")

Then they fed the outfitted rats to captive boa constrictors and measured what happened to the lab rats.Surprisingly, the pressures at which the snakes cinched against the rats weren't all that remarkable. But then again, they don't need to be.

Once blood flow ceases, organs with high metabolic rates—such as the brain, the liver, and the heart itself—begin to shut down. Doctors call this ischemia.

Snakes call it lunch.

An Evolutionary Advantage

The team theorizes that killing by circulatory arrest has given all constricting snakes—which includes pythons and anacondas—an evolutionary advantage. The quicker the snakes can disable their prey, the lower the chance the predator will get hurt in the process.

"That absolutely makes sense," says Paul Rosolie, a conservationist who has spent the last decade working with anacondas.

"Almost every time an anaconda takes something down, it's putting its face on that animal," says Rosolie, who wasn't involved in the new research.

"If it doesn't get the attack exactly right, something big like a capybara can chew right through the body of an anaconda."

Watch a video of an anaconda stalking a capybara.

Anaconda Hunts
When you're an anaconda, you don't need venom to take down your prey, even if it's the world's largest rodent, a capybara, weighing nearly 100 pounds (45 kilograms)!

Ectotherm's Revenge

As interesting as his revelation is, Boback says there's still much we don't know.

For instance, there's evidence that boa constrictors have a tougher time killing ectotherms, animals such as lizards and snakes that rely on external heat to regulate their body temperatures.

During a recent expedition to Honduras, for instance, Boback and several other scientists observed a boa constrictor attacking a spinytail iguana. After the snake constricted its prey for an hour, the team collected both animals—assuming the iguana was dead—and went to bed.